1. Field of the Invention
The present invention relates to a switching power supply apparatus capable of improving its power conversion efficiency to reduce power usage.
2. Description of the Related Art
It is desirable in recent years to reduce power loss when an apparatus is not used in terms of energy saving. Japanese Unexamined Patent Application Publication No. 2002-62952 discloses an apparatus that stops supply of power from a power supply unit, such as an analog-to-digital adapter, to a system at power-off or at light-load and supplies the power from a battery that is charged to the system to reduce the power loss.
However, the apparatus described in Japanese Unexamined Patent Application Publication No. 2002-62952 performs control so as to switch the supply of the power from the power supply unit to the battery depending on the state of the load, regardless of the state of the battery. Accordingly, there are problems in that it is not possible to effectively use the energy of the battery and, thus, the reduction effect of the power usage is small. In addition, the apparatus described in Japanese Unexamined Patent Application Publication No. 2002-62952 has problems in that, since it is necessary to provide a circuit to control charge and discharge of the battery or a circuit to control output voltage from the battery, the power conversion efficiency at the light-load is degraded to increase the annual power usage, compared with a case in which the power is directly supplied from the power supply unit to the load. Furthermore, since the control is performed so as to switch the supply of the power from the power supply unit to the battery depending on the state of the load, the charge and discharge of the battery is frequently repeated if the state of the load is frequently varied. As a result, there is a problem in that the battery is deteriorated to shorten the life of the battery.